Triplet anisotropy decay will be used to measure the rotational Brownian motion of DNA and related protein complexes such as RNA polymerase, nucleosomes and chromatin. A systematic and deductive approach will be used with stron support of theory to understand the torsional and bending rigidity of DNA alone and when complexed in biologically important systems. The ultimate aim of this work is to use physical techniques in order to understand the physical, molecular mechanisms of DNA transcription and replication. The technique used offers the advantage of sensitivity to motions over a time scale from nanoseconds to milliseconds, and at nanomolar concentrations of labels so that in vivo measurements should be possible.